When a bare IC chip is connected to a circuit board by flip-chip method, a separation must be provided between the IC chip and the circuit board in order to prevent occurrence of short-circuiting at scribe lines that are not covered with passivation film. Connecting bumps of height of about 10 μm to 80 μm are therefore commonly formed on the IC chip (FIG. 3 to FIG. 5).
In the embodiment shown in FIG. 3, the gold bumps 31 of an IC chip 32 having gold bumps 31 formed by the stud bump method and a connection terminal 34 of a circuit board 33 are thermo-compression bonded using an anisotropic conductive adhesive 37 (film or paste) obtained by dispersing conductive particles 35 in a binder 36. Also, in the embodiment shown in FIG. 4, the gold bumps 41 of an IC chip 42 having gold bumps 41 formed by the stud bump method and a connection terminal 44 of a circuit board 43 are thermo-compression bonded using an insulating adhesive material 45 (film or paste).
It should be noted that, in the embodiments of FIG. 3 and FIG. 4, the adhesive force between the IC chip and the circuit board depends on the coagulative force of the binder (adhesive component) in the anisotropic conductive adhesive (insulating adhesive), since there is no mutual metallic bonding between the bumps 31 (41) and the connecting terminals 34 (44).
Also, in the case of the embodiment of FIG. 5, connection of solder bumps 51 and connecting terminals 54 is achieved by bringing the flux-treated connecting terminals 54 of a circuit board 53 into contact with the solder bumps 51 of an IC chip 52 formed with solder bumps 51 by a solder paste printing/reflow method or other method, and heating to above the melting point of the solder, where the gap between the IC chip 52 and the circuit board 53 is filled with an underfilling agent 55. In this case, usually, a washing operation is performed in order to remove the flux before filling with the underfilling agent 55.
However, the embodiments of FIG. 3 to FIG. 5 all presuppose the formation of bumps on the IC chip, which are costly to produce, so there are the problems that the freedom of the IC chip shape is lowered and it is difficult to reduce the cost of effecting connection between the IC chip and the circuit board.
Since, in the embodiments of FIG. 3 and FIG. 4, no metallic bonding is achieved between the bumps 31 (41) and the connecting terminals 34 (44), the adhesive force between the IC chip and the circuit board must depend on the coagulative force of the binder (adhesive component) in the anisotropic conductive adhesive (insulating adhesive). Thus there are the problems that reliability of connection in the case of the embodiment of FIG. 3 that employs an anisotropic conductive adhesive can be guaranteed, but in the case of the embodiment of FIG. 4, which does not employ an anisotropic conductive adhesive, the reliability of adhesion is lower than in the case of metallic bonding.
Furthermore, in the case of the embodiment of FIG. 3, with miniaturization of the bump pitch and miniaturization of the bump size, there is the problem that the risk of occurrence of short-circuiting is increased if the content ratio of conductive particles 35 in the anisotropic conductive adhesive 37 is increased in order to ensure the presence of such conductive particles 35 between the bumps 31 and connecting terminal 34. A further problem is that the cost of connection between the IC chip 32 and the circuit board 33 is increased due to the comparatively high cost of procurement of the conductive particles 35. In the case of the embodiment of FIG. 4, the bumps 41 and connecting terminals 44 are directly press-fixed without interposing conductive particles between the bumps 41 and the connecting terminals 44, so there is a problem of stress concentration at the joints, which further lowers connection reliability. Also, since the pressure during press-fixing must be high, there is a possibility of the IC chip or circuit board sustaining comparatively large-scale damage.
On the other hand, in the case of the embodiment of FIG. 5, although comparatively satisfactory connection reliability is achieved due to the metallic bonding between the solder bumps 51 and the connecting terminals 54, there is the problem that, if the bumps are made sufficiently large to ensure that metallic bonding is formed, it is difficult to make finer the pitch of the solder bumps 51. Additional problems are that a flux F washing step and underfilling agent 55 filling step are added.
The present invention was made in view of the above problems of the prior art. Its object is to make it possible to join an IC chip and a circuit board when connecting a semiconductor device such as a bare IC chip with a circuit board by the flip-chip method, with high reliability and low cost without forming bumps on the semiconductor device, while suppressing short-circuiting, lowering connection costs, suppressing stress concentrations at the joints and reducing damage of the IC chip or circuit board.